Substitutes for plasma and other blood components are designed to replenish the BCC, maintain its aggregate state, replace certain blood functions (leukocyte mass, plasma preparations, platelet concentrate), maintain water and electrolyte balance, oncotic blood pressure, and correct acid base balance. Drugs of this group are also used as detoxifying agents that have the ability to bind various toxic substances and accelerate their excretion from the body, as well as reduce the aggregation of blood corpuscles in the capillaries.
Plasma substitutes themselves perform only one function – maintaining the necessary BCC. They must meet a number of requirements:
- do not pass through the histohematogenous barriers and do not penetrate from the vessels into the tissues;
- maintain sufficient and stable osmotic pressure;
- have a minimal and prolonged metabolism, accompanied by the formation of neutral products or metabolites that are included in normal metabolic reactions, or are intensely filtered with urine;
- not antigenic and pyrogenic.
Plasma substitutes include donated blood plasma (natural plasma substitute), dextrans and electrolyte salt solutions (crystalloid solutions).
Plasma contains all the components of the liquid part of human blood, but requires special storage methods and is not indifferent to the donor organism in antigenic terms.
Dextrans are solutions of polysaccharides from cultures of a number of bacteria, devoid of antigenic properties. Dextrans can have different degrees of polymerization and, accordingly, different molecular weights; from them can be obtained plasma-substituting solutions for various functional purposes. Solutions containing high molecular weight dextrans are used mainly as hemodynamic agents, while those with lower molecular weight are used as correctors of the rheological properties of blood. When introduced into the blood stream, dextrans increase oncotic pressure and enhance the processes of fluid transfer from tissues to the bloodstream. They increase urine output, thereby facilitating detoxification processes. Undergoing partial hydrolysis in the body, dextrans are excreted mainly by the kidneys (renal failure is a limitation to their use).
Crystalloid solutions (Ringer’s, Ringer’s acetate, Hartmann’s) contain various combinations of salts (sodium chloride, sodium bicarbonate, sodium acetate, calcium chloride, potassium chloride), as well as glucose in concentrations close to physiological. The action of saline solutions is aimed at correcting dehydration, electrolyte content, hydrogen ion concentration and, accordingly, acid-base balance. In the absence of significant losses of electrolytes, 5% (isotonic) dextrose solution is administered to correct hypovolemia.
A number of pathological conditions (obstruction of the esophagus, impaired absorption from the intestine, severe intoxication, etc.), operations on the stomach and intestines necessitate parenteral administration of nutrients, primarily proteins. Plasma substitutes (albumin 20–25%, dextrose 20–50% solutions) can be used in such situations as drugs for parenteral nutrition provide substrate for many enzymatic processes, dextrose – energy metabolism. However, it should be borne in mind that parenteral administration of proteins can lead to sensitization of the body with the development of anaphylactic reactions with repeated injections.
Substitutes for plasma and other blood components are used mainly for the treatment and prevention of shock of various origins, normalization of blood pressure and improvement of hemodynamic parameters. They are used for blood loss, burns, and other conditions accompanied by dehydration and hypovolemia, for the prevention of postoperative and post-traumatic thromboembolism, with intoxications of various origins. Dextrose preparations (20-40% solution) are also used to correct hypoglycemic conditions. For the purpose of parenteral nutrition, these drugs are used to provide the body’s current energy consumption and regenerative processes in cells, when natural nutrition is impossible for a number of reasons.
Below is a list of substitutes for plasma and other blood components: